Table 2.

Outlier Analysis.

Probable cause	Number	%
Device calibration	90	25.2
Optical signal variability	94	26.3
Temperature/pH changes	50	14.0
Patient activity	39	10.9
Physiological effect	22	6.2
Device malfunction/use error	10	2.8
Interfering medications	9	2.5
Suspect reference sample	1	0.3
No cause attributed	42	11.8